The present disclosure describes systems and techniques relating to wireless communications.
Wireless communication devices can use one or more wireless communication technologies such as orthogonal frequency division multiplexing (OFDM) or code division multiple access (CDMA). In an OFDM based wireless communication system, a data stream is split into multiple data substreams. Such data substreams are sent over different OFDM subcarriers, which can be referred to as tones or frequency tones. Various examples of wireless communication devices include mobile phones, smart phones, wireless routers, wireless hubs, base stations, and access points. In some cases, wireless communication electronics are integrated with data processing equipment such as laptops, personal digital assistants, and computers.
Wireless communication systems provide mechanisms for data retransmission such as automatic repeat request (ARQ) and hybrid ARQ (HARQ). In ARQ, error detection information bits, e.g., cyclic redundancy check (CRC) bits or checksum bits, are included in a data transmission. A wireless communication device can use error detection bits to detect one or more errors in a decoded version of a received message. In HARQ, error correction bits, such as forward error correction (FEC) bits, are included in a data transmission. A wireless communication device can use error correction bits to correct one or more errors in a decoded version of a received message. A data transmission can include FEC bits and error detection bits. A wireless communication device can use a coding technique such as Reed-Solomon coding, convolutional coding, or turbo coding to encode and decode data. Encoding data may compensate for noise on a wireless communication channel.
When a message is received, the error detection information can indicate a success or a failure. A decoded message that fails error detection is deemed to have failed decoding, whereas a decoded message that passes error detection is deemed to have been successfully decoded. The wireless communication device can use error detection information to select between sending an acknowledgement (ACK) or a negative acknowledgement (NACK) to the device that transmitted the message. When an ACK is received at the original transmitter, it knows the message was received successfully. When a NACK is received, it knows that the message should be retransmitted.
However, in some cases, the message is received successfully and the ACK is sent, but the original transmitter fails to successfully receive the ACK. Thus, the transmitter resends the message, and the receiver processes the repeated message. For example, in a cellular network, a base station, such as an evolved Node B (eNB), can retransmit a message that was previously received and successfully decoded by a wireless device, often referred to as user equipment (UE). The UE then decodes the retransmitted message as before, including the data portion therein.